I am 99.9% sure I put the oil gasket on the oil filter canister. But When I got done, I noticed two gaskets laying on the ground

. It was a ******************** to get off, but when I put it on I heard it kind of squeak(like rubber on plastic). If I have to I will drain the oil out and check.
How screwed am I if I didn't put one in?
What is the worst that could happen?
Any expert opinions would be appreciated.
Also, I put 9 1/2 quarts in and it still says I am 2 or 3 bars from full on my Boxes cpu. What is that all about?